This invention relates to a medical appliance for pressure measurement in a blood vessel, comprising an elongated flexible shaft with a proximal area and a distal area, a lumen extending through the shaft from the proximal area to the distal area thereof, aperture means in the distal area of the shaft for the entry of a pressure medium into the lumen, and stiffening means in the lumen for stiffening shaft portions with full available shaft stiffness.
The monitoring of fluid pressures during intravascular procedures such as angioplasty gives valuable information to the cardiologist to assess both coronary myocardial flow reserve and collateral blood flow.
Attempts have been made to develop hollow guide wire systems which allow for the measurement of the fluid pressure at the distal end of a catheter from the proximal end thereof. The problem with that kind of pressure measuring guide wire is to provide an uninterrupted lumen throughout the shaft which has to be highly flexible to conform with tortuous pathways of the blood vessels; and simultaneously, the shaft must have an acceptably high stiffness to have pushability and assure torque transmission as well as it must have a very good kink resistance to avoid the risk of constrictions which could result in modification of the advance of pressure waves through the lumen.
For example U.S. Pat. No. 5,050,606 describes a flexible guiding member which can be utilized for monitoring of fluid pressure during intravascular procedures, or which can be utilized for directing inflation fluid to the interior of a dilatation balloon during angioplasty procedures. This guiding member has a main elongated tubular shaft with an inner lumen extending therethrough to an axial port in the distal end thereof. A core member is secured within the inner lumen and extends out of the distal end of the shaft. A tubular extension is disposed about the portion of the core member which extends out of the shaft and is secured at its proximal end to the distal end of the shaft; its distal end is provided with pressure monitoring ports. The proximal end of the core is secured within the distal end of the shaft by means of a weldment and this core wire has a cross-sectional area substantially less than the smallest transverse cross-sectional area of the inner lumen of the shaft. When the system is utilized in an independent guide wire configuration, the distal end of the tubular extension is bonded to the core member extending therethrough and also to a flexible body such as a helical coil which is disposed about and secured to the portion of the core which extends out of the distal end of the tubular extension. When the system is utilized in a so-called low profile steerable dilatation catheter configuration, an inflatable balloon is secured by its proximal end to the distal end of the tubular extension, and the distal end of the balloon is sealed about the portion of the core which extends out of the distal end of the tubular extension; the proximal end of the balloon is also bonded to the core. The tubular shaft is stiff and the tubular extension is diametrically relatively rigid to prevent kinking but it is longitudinally more flexible than the shaft because it is this distal portion of the system which must be advanced out of the guiding catheter into the patient""s tortuous vasculature. The proximal end of the tubular shaft may be provided with a removable adapter to direct inflation fluid into the inner lumen thereof. U.S. Pat. No. 4,964,409 describes the same device as U.S. Pat. No. 5,050,606 which is referred to hereinbefore.
European Patent Application 0 313 836 shows a pressure monitoring guide wire having a tubular shaft with an axially extending lumen. A tubular member extends axially from the distal end of the shaft in axial alignment with the lumen thereof, such tubular member having its proximal end received within the distal portion of the shaft. A spring coil distally ending in a tip extends axially from the shaft and surrounds the tubular member and the shaft, the spring coil and the tubular member are soldered together at their connection areas. A solid core extends from the distal end of the tubular member within the coil, with its proximal end welded to the tubular member and its distal end welded to a disk located within the coil. A safety wire connects the disk to the tip of the coil and pressure monitoring holes are formed in the wall of the tubular extension, near the distal end thereof. Operation of this guide wire is as follows: a dilatation catheter with an inflatable balloon towards its distal end is inserted into a blood vessel through a guiding catheter and advanced into the desired artery along the guide wire which is positioned so that the pressure monitoring holes are positioned beyond the distal end of the dilatation catheter when the balloon is in position to dilate a lesion. With the balloon dilated, the pressure on the distal side of the balloon can be monitored at the proximal end of the guide wire through the pressure monitoring holes and the luminal openings in the shaft and tubular member. An adapter may be attached to the proximal end of the shaft for attachment to a stopcock manifold. If an extension wire is needed, the adapter may be removed and an extension shaft having a long tapered tip may be press-fit into the proximal end of the tubular shaft. The original catheter may then be removed and replaced with an alternate catheter. The extension wire is then removed and the adapter is replaced on the proximal end of the guide wire for pressure monitoring. U.S. Pat. No. 4,953,553 also refers to such a device.
Another approach is shown in the document EP 0 419 277 which describes a guide wire for use in measuring a characteristic of liquid flow in a vessel, comprising a flexible elongate element in the form of a tube with a core wire provided therein to provide additional rigidity and torque ability to the guide wire. The core wire extends beyond the distal end of the tube into a coil spring assembly which is soldered to the tube and to the core wire. The coil spring assembly is formed of two parts which are screwed together and the assembly is soldered to the core wire at the region where the two portions of coil are screwed together. A safety wire extends from the joint of the two coils to the distal extremity of the coil spring assembly where it is secured to a transducer carried by the distal end of the coil spring assembly. Front and rear contacts are provided on the transducer and are connected to a two conductor wire which extends rearwardly and interiorly of the coil spring assembly and further extends into the tube between the core wire and the interior of the tube to get out of the tube for connection to a male connector. According to a variant, an insulating sleeve may form a tight fit with the exterior surface of the core wire and it may also fit within the tube to insulate the core from the tube so that the core and tube may serve as separate and independent electrical conductors.
European Patent Application No. 95105777.7 filed Apr. 18, 1995, describes a pressure measuring guide wire comprising an elongated hollow shaft the proximal end of which is for connection to a pressure monitoring equipment. The distal area of the shaft comprises a plurality of elongated slots formed in the shaft wall for pressure medium entry, whereby the resistance to kinking of that area is smaller than that of the proximal area of the shaft which is devoid of slots. A coil, possibly made of a radiopaque metal, is located inside the shaft under the slots for supporting the wall and slot structure and for providing a radiopaque reference to that area. A core member is located within the coil with proximal and distal ends formed to abut longitudinally with the corresponding ends of the coil in order to stiffen the coil. In a variant, the core member may have its proximal end extended by a wire which goes proximally along and out of the lumen of the shaft. In that case, the supporting coil may be placed under the slots only for insertion of the guide wire to assure resistance to kinking, when the guide wire is properly located, the supporting coil and wired core assembly may be removed from the guide wire to maintain the shaft lumen free of obstructions for pressure measurements.
It is an object of this application to propose a medical appliance for pressure measurement in a blood vessel which is easy and inexpensive to manufacture, which has an appreciable handling versatility while providing very good qualities of resistance, steerability and pushability, and which allows a smooth advance of pressure waves in a very low profile guide wire configuration.
Accordingly, with the stiffening means consisting of an independent wire removably extending within at least a portion of the lumen and proximally of the proximal area of the shaft, it becomes possible to select a basic stiffness and floppyness for the shaft and to either withdraw the independent wire from the shaft lumen and to replace it by another independent wire having other characteristics, or to displace the independent wire along the shaft lumen. The stiffness and flexibility of the shaft as well as its resistance to kinking and floppyness are thus fully selectable and assured, and they may be modulated by the independent wire without any detriment to the selected shaft configuration or intrinsic qualities, and most of all without increasing its outer size. The shaft therefore may be devised as a mere tubing with extremely thin walls which can be safely and efficiently advanced through tortuous and narrow vessels as well as through acute stenoses. For pressure measurements, it suffices to withdraw the independent wire to take advantage of a lumen which is fully free of any obstruction, whereby a better frequency behavior for the fluid medium. And as the shaft lumen is always free of obstruction for pressure measurement, it is possible with a thin walled shaft to have a shaft with a very low profile and a relatively large lumen assuring a good flow of the fluid medium for pressure measurements.
When the independent wire is coiled, it is possible to assure the required stiffness for the shaft while having a greater elasticity for the independent wire, which may be of further help for extremely thin walled shafts.
When the independent wire has an outer transverse size which decreases from a proximal portion to a distal portion thereof, a greater modulation of stiffness and floppyness is achieved for the shaft which can be further modified by displacement of the independent wire along the lumen or its mere replacement by another wire similarly devised.
With an independent wire frictionally extending within the lumen, it is possible to achieve the lowest profile for the tubular shaft because of the closest relationship between independent wire and shaft while retaining all the other characteristics of the appliance. Simultaneously, there is the advantage that the independent wire is retained in the position chosen by the practitioner for particular shaft stiffness modulation.
Where a luer-lock is removably mounted on the shaft, the practitioner has the great advantage that he can use the pressure measurement appliance as a conventional guide wire. After insertion of the luer-lock equipped appliance proximally and distally of a stenosis for determining the pressure gradient, it suffices to remove the luer-lock for inserting a catheter such as a balloon catheter over the appliance which then acts as a pure guide wire which is already in place for guiding the balloon catheter exactly at the place required. Time and cost saving is achieved and extra manipulations for inserting a new guide wire after pressure measurement and withdrawal of the pressure measuring device are avoided while maintaining all the advantages of the appliance which becomes an efficient and low profile purpose device.
When abutment means on the independent wire are securing an end position of the independent wire in the lumen, the practitioner may simply insert the independent wire into the shaft without particular precautions as to its longitudinal position within the lumen, knowing that the independent wire will not go beyond a pre-fixed position in the lumen. He can also use that pre-fixed position as a reference for further modulation of the shaft stiffness by displacement in the independent wire.
In sum, the present invention relates to a medical appliance for pressure measurement in a blood vessel. It has an elongated flexible shaft with a proximal area and a distal area, a lumen extending through the shaft from the proximal area to the distal area thereof, aperture means in the distal area of the shaft for the entry of a pressure medium into the lumen, and stiffening means in the lumen for stiffening shaft portions with full available shaft stiffness. The stiffening means may be an independent wire removably extending within at least a portion of the lumen and proximally of the proximal area of the shaft. The independent wire may be coiled, and may have an outer transverse size which decreases from a proximal portion to a distal portion thereof. The independent wire may frictionally extend with the lumen. The medical appliance may have a luer-lock removably mounted on the shaft. Abutment means on the independent wire may secure an end position of the independent wire in the lumen.